PTEN is a tumor suppressor that is deregulated in a large number of human cancers to activate the oncogenic phosphoinositide-3 kinase (PI3K) pathway. Inactivation of PTEN leads to multiple phenotypes including cancer, changes in stem cell biology and alteration of fundamental processes such as proliferation and apoptosis. We have recently determined that the PI3K pathway activates the transcriptional repressor NFIL3/E4BP4. NFIL3 is over expressed in human breast cancers lacking PTEN. Moreover, over expression of NFIL3 is seen in multiple types of poor-prognosis cancer. We have shown that NFIL3 binds and recruits HDAC2 to promoters to deacetylate histones and silence genes and even represses a recently recognized pool of nuclear FOXO proteins at multiple FOXO target genes. Our findings have broad implications that suggest that NFIL3, which represses numerous non-FOXO targets, could mediate reprogramming of chromatin as a consequence of PTEN mutation. This application will use a combination of biochemistry, signal transduction, mouse genetics, and cancer cell biology to address the following goals 1) to understand the mechanism by which NFIL3 alters the epigenetic regulation of target genes, 2) to determine the contribution of NFIL3 to changes in gene expression and chromatin modification caused by genetic ablation of PTEN, 3) to demonstrate the contribution of NFIL3 to tumor and other phenotypes due to PTEN mutation in mice and cells, and 4) to define how NFIL3 is regulated by PTEN and its implication for PI3K- based cancer therapy.